Bayowa Et Al
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Ife Journal of Science vol. 16, no. 3 (2014) 353 INTEGRATION OF HYDROGEOPHYSICAL AND REMOTE SENSING DATA IN THE ASSESSMENT OF GROUNDWATER POTENTIAL OF THE BASEMENT COMPLEX TERRAIN OF EKITI STATE, SOUTHWESTERN NIGERIA. 1Bayowa O.G., 2Olorunfemi M.O., 3Akinluyi F.O., and 4Ademilua O.L 1Department of Earth Sciences, Ladoke Akintola University of Technology, Ogbomoso, Nigeria. 2Department of Geology, Obafemi Awolowo University, Ile-Ife, Nigeria. 3Department of Remote Sensing and GIS, Federal University of Technology, Akure, Nigeria. 4Department of Geology, Ekiti State University, Ado-Ekiti, Nigeria. Corresponding Author E-mail:[email protected]; [email protected] (Received: 8th August, 2014; Accepted: 12th August, 2014) ABSTRACT Hydrogeophysical investigation as well as analyses of hydrogeomorphological, geologic/hydrogeologic, electrical resistivity and borehole data had been carried out in the Basement Complex terrain of Ekiti State, Southwestern Nigeria. This was with a view to classifying the area into different groundwater potential zones. The VES interpretation results were used for aquifer identification; aquifer geoelectric parameter determination and for the calculation of the overburden coefficient of anisotropy. Hydrogeomorphological, lineament density, lineament intersection density and overburden coefficient of anisotropy thematic maps were produced and integrated for the classification of the study area into different groundwater potential zones. The reliability of the groundwater potential map was checked with the existing groundwater yield data. The weathered and fractured basement constituted the main aquifer units. The groundwater yields of boreholes located within quartzitic rocks had a mean of 1.56 l/s while the mean groundwater yield from metasediment (schist) was 1.14 l/s. The study area was characterized into five different groundwater potential zones which were very low, low, moderate, high and very high. Ijelu-Ekiti, Ayede, Ipao, Ikole, Oye. Ayegbaju, Ofale-Ijero and Omuo-Ekiti were classified as very low groundwater potential areas while low groundwater potential was established in Ijesa-Isu, Iludofin, Iyemero, Esure, Otun, Osi, Iropora, Ifaki, Ikun, Ijero, Ado, Emure and Ise/Orun. Igbara-Odo, Ilawe, Ikogosi, Ido, Ipole-Iloro, Ipere, Ayetoro, Ikoro, Ifisin, Ilogbo, Isinbode, Erinmope and Iwaro fall within moderate groundwater potential zones. High groundwater potential was recorded in Ijan, Okemesi, Aramoko, Ilemeso, Ikere, Etisun and Itawure. Efon-Alaaye and Ilumoba fall within very high groundwater potential zone. The groundwater potential of Ekiti State is generally of very low–moderate level rating. There were however few areas with high to very high groundwater potential. Keywords: Basement Complex, Hydrogeophysics, Remote Sensing, Groundwater Potential, Ekiti State. INTRODUCTION anisotropy and groundwater yield in the basement There has been a progressive increase in the complex area of the southwestern Nigeria. Their population of Ekiti State with the attendant findings include amongst others that the increase in the demand for potable water for both groundwater yield generally increases with domestic and industrial usages. The gross increase in the overburden coefficient of inadequacy of public water supply has made anisotropy. Teme and Oni (1991) used remote groundwater development through hand dug wells sensing techniques to detect groundwater flow in and boreholes inevitable. However, the success of fractured media in hard rock terrain. They used groundwater development programme is aerial photographs and radar imageries to predicated on good understanding of the adequately locate and delineate the extent and geomorphological, geological, hydrogeological frequency of these fractured systems thus making and geophysical characteristics of the basement it possible for the siting of productive boreholes at complex terrain. These characteristics are required approximately predetermined localities within the for the assessment of the groundwater potential. basement areas. Mohammed (1992) carried out a Groundwater investigation is therefore often geophysical investigation for groundwater multidisciplinary in approach and could involve development at the Federal University of terrain analysis, geology/hydrogeology, remote technology, Akure.His conclusion was that deep sensing and geophysics. Olorunfemi et al., (1991) weathered zones and fractured or brecciated investigated the relationship between electrical basement which are characterized by relatively low 354 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater resistivity values constitute the main aquifer unit in mainly an upland zone rising over 250 metres the area. Salem (1999) submitted that fluid above the sea level and has a rhythmically transmissivity (layer thickness x permeability) and undulating surface. The area enjoys tropical electric transverse resistance (layer thickness x climate with high rainfall of up to 1600 mm and is resistivity) are important parameters in characterized by two distinct seasons (Ayoade groundwater and hydrocarbon exploration. The 1988). These are the rainy season (April-October) and the dry season (November-March). determination of these parameters provides a o o good knowledge of the potential of porous media, Temperature ranges between 21 and 28 C. The because they relate fluid flow to electric current mean monthly relative humidity is less than 70%. conduction in terms of layer thickness, The South-Westernly wind and the North-East permeability and resistivity. The author Trade wind blows during the rainy and dry established a direct relationship between fluid (Harmattan) season respectively (http://ekitinigeria.net). The vegetation of the area transmissivity and the electric transverse is the rain forest type. Tropical forest exists in the resistance, with coefficients of correlation of 0.99 south. This is characterized by dense evergreen (for aquifers) and 0.94 (for reservoirs) and forest of tall trees with thick vegetation. However, suggested that an increase in both parameters Guinea Savannah occupies the northern indicate presence of zones of high fluid potential periphery (http://ekitinigeria.net). within the aquifers and the reservoirs. Ademilua (1997) attempted to classify both Ondo and Ekiti Geology States into different groundwater potential zones The study area is underlain by the Precambrian but was constrained by few VES data points as well rocks of the Basement Complex of Southwestern as limited sampled localities. Hence, the Nigeria (Figure 2). The basement rocks are groundwater potential map produced by the concealed in places by a variably thick overburden. researcher could not have been representative. A The major lithologic units according to Rahaman preliminary assessment of the groundwater (1976, 1988) are the migmatite-gneiss complex; potential based on terrain and satellite imagery the older granites; the charnockitic rocks; the analyses had been undertaken by Bayowa et al., slightly migmatised to unmigmatised paraschists 2014b. There is therefore the need for detailed and metaigneous rocks and the assessment of the groundwater potential using unmetamorphosed granitic rocks. The migmatite- integrated hydrogeomorphological, gneiss complex is composed mainly of early ,geological/hydrogeological (involving recent gneiss, mafic and ultramafic bands and the granitic satellite imageries covering state) and geophysical or felsic components. The rock type is the most data acquired across the state. widespread, covering about half of the study area (Figure 3). The older granites comprise the The Study Area porphyritic-biotite granite and the medium-coarse The study area lies within Latitudes 7º 15' 00" and grained granite gneiss. The charnockitic rocks are 8º 10' 00" North of the Equator and Longitudes 4º composed of quartz, alkali feldspars, plagioclase, 45' 00" and 5º 50' 00" East of the Greenwich orthopyroxene, clinopyroxene, hornblende, Meridian. Ekiti State has 16 Local Government biotite and accessory amount of opaque ore Areas (Figure 1). Some of the major towns in apatite, zircon and allanite. The slightly Ekiti-State include Ado-Ekiti, Efon-Alaaye, migmatised to unmigmatised paraschists and Aramoko, Ikole, Ikere, Ijero, Ise, Otun, Ido, metaigneous rocks consist of pelitic schists, Emure, Ifaki, Iyin, Igede, Ilawe, Ode, Oye, Omuo, quartzites, amphibolites, talcose rocks, Ilupeju, Ikoro, Igogo, Iye, Ijesa-Isu, Ayedun, metaconglomerates, marbles and calc-silicate Okemesi, Igbara-Odo, etc. Its capital is located at rocks. The umetamorphosed granitic rocks Ado-Ekiti. manifest as dolerite dykes, pegmatites and quartz veins. Physiographically, the state is composed of hilly terrain and Plains with isolated hill locks. According to http://ekitinigeria.net, the area is Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater 355 Figure 1: Map of Ekiti State showing the Local Government Areas. (Digitized from Administrative Map of Ekiti State, 2000). Figure 2: Geological Map of Nigeria (Digitized from Ajibade and Umeji, 1989) 356 Bayowa et al.: Integration of Hydrogeophysical and Remote Sensing Data in the Assessment of Groundwater Figure 3: Geologic Map of Ekiti-State (Digitized from Ademilua, 1997) Hydrogeology of water into larger river valleys. Within the The hydrogeology of an area is controlled by such weathered zone, discontinuous water table occurs factors as geology, structures